(a) Field of the Invention:
This invention relates to a focal plane shutter for cameras and more particularly to the supporting structure of shutter blades in a focal plane shutter wherein shutter blades made of a plural number of opaque thin plates move parallelly with respect to a plane including an exposure aperture in order to open and close the exposure aperture.
(b) Description of the Prior Art:
An example of this kind of conventional focal plane shutter for cameras is known by U.S. Pat. No. 4,024,555. FIG. 1 shows the conventional example wherein the shutter includes an opening blade assembly O and closing blade assembly C arranged in the relation of mirror images with each other between a base plate 1 having an exposure aperture 1a and a cover plate 10 having an aperture 10a coinciding with the exposure aperture 1a. The opening blade assembly O comprises a light interrupting blade group including at least first blades 3a to 3d and a second blade 3e to open and close the exposure apertures 1a and 10a, a first arm 4a pivoted to the base plate, first blades and second blade respectively and a second arm 4b pivoted to the base plate, first blades and second blade respectively so as to form a parallel link mechanism in cooperation with the first arm. The closing blade assembly C is substantially of the same structure as of the opening blade assembly O. The pivoting structure of the first arm 4a and second arm 4b to the base plate 1 are shown with an enlarged scale in FIG. 2. That is to say, the space formed between the base plate 1 and cover plate 10 integrally coupled through screws S is so narrow that, for example, the arm 4a is pivoted by fitting a shaft 2a stood on the base plate 1 into a bearing sleeve 5 calked to the arm 4a and the arm 4b is pivoted by fitting a shaft 2b stood on the base plate 1 into a hole 4b' formed in the arm 4b. The pivoting by fitting the shaft 2a into the bearing sleeve 5 is comparatively so large in the dimension in the radial direction of the shaft 2a that, in order to avoid the interference of this pivoting part with the pivoting parts of the blade group to the arms 4a and 4b, the above mentioned structure is adopted. However, this structure includes a disadvantage that the pivoting by fitting the shaft 2b into the hole 4b' is lower in the durability than the pivoting by fitting the shaft 2a into the bearing sleeve 5. This disadvantage will become a very grave problem in case the shutter speed is required to be high and the focal plane shutter is desired to be endurable to a high speed operation.